This invention generally pertains to a connector for use in coupling a motor drive shaft to a driven member, and more specifically, to a universal style coupling for connecting a motor drive shaft to a driven member such that the coupling accommodates misalignment between the drive shaft and the driven member while minimizing a noise associated with rotation of the driven member by the motor drive shaft.
In many portable motor-driven devices, small direct current (DC) motors are connected to rotatably driven shafts using solid metal couplings. Such couplings typically comprise a short section of thick-walled tubing having two radially-extending threaded orifices formed in the wall of the tubing, adjacent to each end. Set screws are threaded into the orifices and are tightened to engage the drive shaft of the motor that is inserted into one end of the coupling, and to secure a driven shaft that is inserted into the other end of the coupling. Even if a fastener locking substance is applied, the set screws often loosen with use, enabling the drive shaft and/or driven shaft to slip within the coupling, causing scoring of the shafts and possible failure of the devices in which the couplings are installed, as the driven shaft will no longer be rotatably driven by the drive shaft.
Couplings are generally available from suppliers in only a limited range of sizes. If the coupling used to join two shafts is too large, it cannot properly connect the shafts and can cause vibration during rotation, because its mass is not symmetrically distributed around the center lines of the two shafts. In addition, conventional couplings generally require that the center lines of the two shafts that are joined be relatively closely aligned. Any misalignment between a motor drive shaft and a driven shaft, even if slight, is likely to cause side loading of one or both the drive shaft and driven shaft, producing increased wear of bearings or journals in which the shafts are rotatably supported. Solid couplings also transmit noise and vibration from the motor to other parts of the device in which they are used.
Ideally, it would be preferable to provide a coupling that is more tolerant of misalignment between a motor drive shaft and a driven shaft. Furthermore, such a coupling should not cause vibration of the assembly or produce noise while in operation. It will therefore be apparent that a simple coupling, which addresses the problems noted above and is relatively low in cost, would be desirable for use in small electric, motor-powered devices.
In accord with the present invention, a coupling is defined for connecting a drive shaft to a driven member. The coupling includes a hollow core nest and two elongate bodies that pass partially through a central aperture within the hollow core nest. One end of the hollow core nest has a plurality of slots formed therein that the posts engage. The posts are sized to correspond to the width of the slots. The end of each elongate body opposite that with the posts has an opening with a cross-sectional size generally corresponding to that of the drive shaft and the driven member. The openings in the elongate bodies for the drive shaft and the driven member are disposed on opposite ends of the coupler.
The central aperture of the hollow core nest is larger in cross-sectional size than that of the elongate body that passes through the central aperture, thereby enabling the coupling to accommodate radial offset and longitudinal axial misalignment between the drive shaft and the driven member. The plurality of slots have a depth which is greater than the corresponding dimension of the plurality of posts, enabling the coupling to accommodate axial movement. The coupler also includes a plurality of spring elements that provide a biasing force for ensuring that the posts of the first and second elongate bodies are positively in contact with one side of the slots of the hollow core nest, thereby substantially reducing a level of noise that would otherwise exist during rotation of the coupling. The coupler is thereby adapted to drivingly couple the drive shaft to the driven member, such that the coupler accommodates misalignment between the drive shaft and the driven member, and as a result, the coupler operates relatively noiselessly.
In one embodiment the plurality of spring elements are integral to the hollow core nest. In this embodiment, the plurality of spring elements are preferably a narrow strip of material disposed within each slot, such that each slot is separated into two sub-slots, one sub-slot being slightly smaller in size than the plurality of posts on the elongate bodies, such that when one of the plurality of posts is engaged into the slightly smaller sub-slot, said narrow strip firmly engages said post into the sub-slot, thereby reducing a noise level associated with loose fitting coupling components. This embodiment includes an end cap disposed at the end of the hollow core nest that covers the slots, preventing the posts of the elongate bodies from disengaging from the slots. Preferably, elastomeric shims are disposed in the sub-slots not engaged by the plurality of posts.
When properly assembled, the plurality of posts of the elongate body connected to the drive shaft drivingly engage the solid side of the sub-slots, and the plurality of posts of the elongate body connected to the driven member are driven by the solid sides of the sub-slots, when the drive shaft is rotated in a preferred forward direction. To aid in the proper assembly of the coupling, markings are provided on the hollow core nest and on the elongate bodies. Also, the nest preferably includes four slots, each slot having a strip that serves as the spring element, and the elongate bodies each include two posts.
In another preferred embodiment, the plurality of spring elements comprise helical coil springs, each having opposed ends that apply the biasing force between a first post on one elongate body and a second post on the other elongate body. In this embodiment, each post includes a hook that engages an end of one of the helical coil springs. The hollow core nest preferably includes a plurality of channels on its outer surface in which the plurality of spring elements are disposed.
In a preferred embodiment, the slots are disposed of at about 90xc2x0 intervals around the hollow core nest. Furthermore, the posts of each elongate body are preferably disposed about 180xc2x0 apart.